`Rotational InertiaCorla Jean Wilson-Hawkins      Bethune Elementary School                               3030 West Arthington                               Chicago, Illinois 60612                               312-534-6890                 Objective:To demonstrate how the resistance of an object to rotation is rotational inertia. Materials Needed:This list is for a class size of 32 students divided into groups.4 ramps                                      4 meter sticks4 cans of broth soup covered with paper      8 100 gm weights4 cans of tomato soup covered with paper     masking tapependulum                                     balance beam and long polehollow wheel                                 solid wheelturn table for turning (if possible - optional)Strategy:To begin the lesson, have the students give you several brainstorming definitions of what they think inertia is.  Next discuss what they think rotational inertia is and write that on the board.  After discussing the vocabulary, have one student from each group sit on the turn table.  Spin them slowly.  Using equal weights or books in their hands have them pull their hands close to their bodies and then extend them away from their body.  As they pull their hands closer to their bodies they will find that they spin faster than they do when their hands are extended outwards.  Use this opportunity to discuss how the distribution of mass makes a difference in the rotational inertia. Next, using your groups, take the 4 meter sticks and tape the 100 gram weights to the bottom of the stick.  Put one on each side and tape around it.  Have students collect data on who could balance it vertically the longest with the weights on the bottom and again with the weights on the top.  Have the students explain why they thought it was easier to balance the weight on the top of the stick versus the bottom.  Some will be good both ways but the norm tends to be with the weights on the top. Using the ramps, have your groups take the soup cans of different contents that are covered with paper and time them as they roll down the ramp.  Have them make a graph charting the time it took and the can that won.  Have them to try to figure out why one can won over the other.  After a thorough discussion, uncover the cans and talk about the contents in the cans and the distribution of the mass. Now take the balance beam and have it properly mounted with the wooden stands on each end.  Have a student walk on the beam with their hands in their pockets, and again with their hands extended holding a long pole or long stick.  Talk about which way was easier to walk.  Again reinforce that it is easier to balance when the rotational inertia is farther away from the axis. For some additional fun, make a pendulum and push it back and forth on a long string.  Ask the children to tell you how it is moving.  Then shorten the string and let them tell you how it is going.  Of course the shorter one moves faster because it is closer to the axis.  At this point the children can make a pendulum for a hands on activity. For a final activity take a ring and a solid disk and roll them down a ramp. They do not have to be the same weight or size because the theory will still prove itself.  Have the children guess which one will come down first.  Explain to them that since the wooden disk is solid, it's mass is closer to the axis than the hollow ring which has all it's mass on the outer rim. Conclusion:The conclusion of this lesson would be to have students explain what we did today in all our demonstrations.  Ask them to tell you what they liked best and what they liked the least.  See if any of your students can think of other examples of rotational inertia that were not used today that can be added to the lesson.   Evaluation:Often times when we do a lot of hands on activities, we fail to reinforce the comprehension version in writing.  My evaluation of this process will be a short quiz that would include all the examples that we had today and to have the children explain them to me.  I would also have them draw some of the demos for me on paper so that I know who really was aware of what was happening in the demonstration.  I would be looking for 90% accuracy on the quiz. Summary:     Event                    Results                    bottles         empty-easy to move             full-hard to move     turntable       mass at center-easy to rotate  mass at edge-harder to do     meter stick     wts on bottom hard to balance  wts on top easy to balance     balance beam    mass at center-easy to fall    mass out-easier to stay     pendulums       short-swings faster            long-swings slower     soup cans       tomato solid-rolls fast        chicken-liquid rolls slower     disk and ring   disk is faster-mass spread     ring is slower-mass all at                         uniformly throughout           the edge (further out)  Reference: Conceptual Physics -  Addison Wesley  Paul G. Hewitt   1986 pg 192-204`